linux-kernel - Re: [PATCH] arm: Handle starting up in secure mode

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Date:	Wed, 26 Aug 2015 11:48:39 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Dave Martin <Dave.Martin@....com>
Cc:	Christopher Covington <cov@...eaurora.org>,
	Mark Rutland <mark.rutland@....com>,
	"Jon Medhurst (Tixy)" <tixy@...aro.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Will Deacon <will.deacon@....com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Nicolas Pitre <nico@...aro.org>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Yingjoe Chen <yingjoe.chen@...iatek.com>,
	Wang Nan <wangnan0@...wei.com>,
	Kees Cook <keescook@...omium.org>,
	Arnd Bergmann <arnd@...db.de>,
	Gregory CLEMENT <gregory.clement@...e-electrons.com>,
	linux-arm-kernel@...ts.infradead.org,
	Paul Bolle <pebolle@...cali.nl>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Nathan Lynch <nathan_lynch@...tor.com>,
	linux-kernel@...r.kernel.org,
	Masahiro Yamada <yamada.m@...panasonic.com>,
	Maxime Coquelin stm32 <mcoquelin.stm32@...il.com>
Subject: Re: [PATCH] arm: Handle starting up in secure mode

On Wed, Aug 26, 2015 at 11:39:42AM +0100, Dave Martin wrote:
> On Mon, Aug 24, 2015 at 09:55:26AM -0400, Christopher Covington wrote:
> > ARM Linux appears to have never been made aware of the ARMv7 security
> > extensions. When CONFIG_ARM_SEC_EXT=y, have it probe for its security
> > state by checking whether CNTFRQ is writeable and potentially make
> > mode changes based on the information. The most features are available
> > from hypervisor (HYP) mode, so switch to it possible. Failing that,
> > prefer non-secure supervisor (SVC) mode to secure supervisor mode.
> 
> Up to now we've steered clear of this, since it's a bit of a fig leaf
> for broken firmware unless Linux actually has some valid use for the
> Security Extensions itself.
> 
> Shouldn't the bootloader or firmware be doing this stuff, and if not,
> why not?
> 
> 
> Some other things that would need to be considered in any case:
> 
>  * SoC-specific setup of the Non-secure view of the system:  This has
>    to happen very early, so making it DT aware is going to be hard --
>    failing that, we are effectively risking bringing back board files.
>    The split in responsibility between firmware/bootloader and kernel
>    needs to be clearly defined and (as far as possible) platform-
>    independent, otherwise we'll have total chaos.
> 
>  * Out of reset, generally the CPU state is only fully defined for the
>    highest exception level.  You probably need to be doing more setup
>    than you're currently doing.
> 
>  * SMP, secondary boot and suspend/resume -- again involving board-
>    specific code.
> 
>  * You need to safely "park" the Secure World before running anything
>    in Non-Secure.  As a minimum, you would need to quiesce any
>    Secure interrupt sources, disable all interrupt traps to Monitor
>    mode, and make sure that the Monitor vectors point somewhere
>    real, so that executing SMC doesn't send the CPU off into the
>    long grass...

Another question is: has this been tested with kexec?

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